Note:  Do not rely on this information. It is very old.

Bog Oak

Bog-Oak, the wood of the common British oak, when, having fallen into peat, it has become stained a deep black by the action of a natural ink formed by the action of the tannin which it contains upon the iron-salts in the peat. It is obtained in considerable quantity below the peat both in Ireland and Scotland, and is used for ornaments. The wood of yew under similar circumstances becomes a deep brown.